Motor vehicle drivers are required to negotiate traffic safely when travelling on public roads. For this reason, cars, trucks and other road-travelling motor vehicles are typically equipped with mirrors positioned both inside and outside the vehicle. The mirrors allow the driver to see a portion of the road behind or beside the vehicle with only a slight shift of the eyes or turn of the head. If other vehicles are visible the driver will be suitably alerted and in position to avoid making an inappropriate move, such as a lane change.
Having an awareness of the presence of neighbouring vehicles is particularly important when changing lanes, either to the left or the right. To change lanes safely the driver needs to ascertain beforehand that there is no vehicle in the adjacent lane. However, for simple reasons of geometry the mirrors that are commonly factory installed in motor vehicles only provide a partial view of the space immediately to the side and towards the back of the vehicle, which needs to be clear to change lanes. The unviewable space, commonly called the “blind spot”, is therefore typically checked by the driver physically turning his or her head to the side in a so called “shoulder check” so that the space can be viewed directly. When it is confirmed that the space is clear and that there is no other vehicle fast approaching, the driver can move their vehicle into the desired lane.
While turning one's head can be a partially effective way to check the blind spot, it also creates a safety risk since it forces the driver to take his or her eyes away from the road directly in front of the vehicle. In particular, there is a risk of a collision with a vehicle in the space ahead if that vehicle brakes or decelerates quickly in the moment that the driver is checking the blind spot. Even if the driver does notice the vehicle in front when his eyes return, it may be too late to stop safely. This risk becomes even more acute when driving conditions are less than optimal, such as in heavy traffic, or when there is poor visibility due to night time darkness or adverse weather conditions such as snow or ice on the road. Further, there will always be drivers with limited or no head mobility due to disability or a stiff neck, as well as people with slower than average reaction times such as seniors. Also, drivers of large vehicles such as trucks that sit high above the road may have difficulty seeing small vehicles occupying the lane on the passenger side. Drivers operating under such conditions are much more susceptible to the risk of an accident when changing lanes. Lastly, even with a shoulder check, portions of the field of view will be unviewable due to door pillars, condensation, snow, and the like. It is desired to reduce the number of checks made of the blind spot to reduce the risk of a dangerous situation arising without changing normal safe driving practices or requirements.
For these reasons various attempts have been made in the past to create a safety device capable of automatically detecting the presence of a target vehicle in the blind spot. If possible, this would reduce the need for a “shoulder check” when a lane change can't occur because the desired lane is occupied by another vehicle, without changing normal safe driving practices or requirements. Ideally the device informs the driver whether the lane is clear or occupied, so that the driver need only shoulder check to confirm the lane is clear to change lanes safely while keeping most of his or her attention on the road ahead.
One known type of detecting device taught in U.S. Pat. No. 5,112,796 to Beggs et al actively emits a signal, for example in a short wavelength infrared region, and then detects the presence or absence of a reflected wave from a target vehicle. Active devices such as this however are relatively complex and need both a transmitter and a receiver. Because of the complexity of the components and the number of elements required, such as electrical connection, power supply, signal emitter, and signal detector, active systems tend to be expensive. Further, failure of any one component means the whole system fails. As well, such systems tend to create false positive alarms, due to reflection of the signal off of stationary objects such as parked cars and the like. As a result, such systems have not been broadly commercially deployed.
Another approach involves the use of a thermal emitted radiation detector of the type found in security system motion detectors. These detectors can be used to passively sense the heat being generated as a matter of course by any target vehicle. Such a detector needs no emitter and therefore has the advantage of a relatively simple and inexpensive design. However, this type of detector requires a change in temperature to create a detectable event and therefore is generally only effective when the target vehicle enters or leaves the field of view of the detector. Target vehicles that are travelling at the same speed as the host vehicle or sensor platform and that remain in a fixed position in the blind spot may become undetectable. Thus, a driver may mistakenly assume a vehicle has passed through the blind spot when in fact it remains there. A lane change in such a case could result in an accident.
This particular issue is addressed in the device described in U.S. Pat. No. 5,668,539 to Patchell, the present inventor. In this device thermal emission readings are obtained from a reference position on the road immediately beside the host vehicle, where it is expected that there will be no other vehicle, as well as from at least one position in the blind spot itself. The reference and other emission readings are compared and a detection event arises if there is a substantive difference between the two values. This device however produces false alarms when there is a variation in road temperature between the reference spot and blind spot, such as the cool area created by a shadow under a bridge on a sunny day. Thus, this prior device also suffers from a statistically small but unacceptably high level of false detection events.
What is needed is a detection system which is simple, inexpensive, and reliable, and which does not produce an unacceptable level of false detection events. In the absence of any solution that addresses the practical problems of detecting a target vehicle in a blind spot under real road, traffic, and weather conditions, tragic and costly accidents due to driver blind spot miscalculation will continue to occur.